1. Output Devices

This week's assignment involves adding output devices to my custom-designed microcontroller board and programming them for functionality. For my final project "Smart Glasses", I need to integrate an LCD display and an audio playback module.

1.1. Audio Playback Module

Hardware Implementation

I selected the MAX98357A - an I2S protocol-based Class D audio amplifier with the following advantages:

• Integrated digital-to-analog converter (DAC)
• 3.2W output power at 4Ω load
• 92% power efficiency

Connection Diagram:

MAX98357A Pin	ESP32-S3 Pin
BCLK	GPIO2
LRC	GPIO3
DIN	GPIO1
GND	GND
VIN	3.3V

Software Development

Core implementation steps:

1. Configure I2S peripheral using ESP-IDF driver
2. Implement audio buffer management
3. Add WAV file decoding capability

Basic playback code:

#include <dirent.h>
#include <stdio.h>

#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "driver/i2s_std.h"
#include "driver/gpio.h"
#include "esp_log.h"
#include "audio.h"

static i2s_chan_handle_t tx_handle = NULL;
void init_speaker(void)
{
    i2s_chan_config_t tx_chan_cfg = I2S_CHANNEL_DEFAULT_CONFIG(I2S_NUM_AUTO, I2S_ROLE_MASTER);
    ESP_ERROR_CHECK(i2s_new_channel(&tx_chan_cfg, &tx_handle, NULL));

    i2s_std_config_t tx_std_cfg = {
        .clk_cfg  = I2S_STD_CLK_DEFAULT_CONFIG(8000),
        .slot_cfg = I2S_STD_MSB_SLOT_DEFAULT_CONFIG(I2S_DATA_BIT_WIDTH_16BIT, I2S_SLOT_MODE_MONO),
        .gpio_cfg = {
            .mclk = I2S_GPIO_UNUSED,    // some codecs may require mclk signal, this example doesn't need it
            .bclk = 2,
            .ws   = 3,
            .dout = 1,
            .din  = I2S_GPIO_UNUSED,
            .invert_flags = {
                .mclk_inv = false,
                .bclk_inv = false,
                .ws_inv   = false,
            },
        },
    };
    ESP_ERROR_CHECK(i2s_channel_init_std_mode(tx_handle, &tx_std_cfg));
}

void app_main(void)
{
    init_speaker();

    while (1)
    {
        i2s_channel_enable(tx_handle);
        i2s_channel_write(tx_handle, (uint8_t *)_acfablab, sizeof(_acfablab), NULL, 1000);
        i2s_channel_disable(tx_handle);

        vTaskDelay(1000 / portTICK_PERIOD_MS);
    }
}

tip

Full implementation available at: openGlasses Audio Module Code

Demonstration:

Advanced Feature: Internet Radio

Implemented a streaming audio client using ESP32's WiFi capabilities:

#include "Arduino.h"
#include "WiFi.h"
#include "Audio.h"
#define I2S_DOUT     1
#define I2S_BCLK      2
#define I2S_LRC        3
Audio audio;
String ssid =    "******";
String password = "******";
void setup() {
  WiFi.disconnect();
  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid.c_str(), password.c_str());
  while (WiFi.status() != WL_CONNECTED){
    delay(100);
    Serial.print*(".");
  }
  delay(1500)
  Serial.print("conneted");
  audio.setPinout(I2S_BCLK, I2S_LRC, I2S_DOUT);
  audio.setVolume(100);
  audio.connecttohost("http://vis.media-ice.musicradio.com/CapitalMP3");
}
void loop()
{
  audio.loop();
}

tip

Change the ssid and password to your own WiFi network.

Key Features:

• Automatic audio buffer management
• Bitrate adaptation
• Error correction for unstable networks

Streaming Demo:

1.2. LCD Display Module

Hardware Integration

Used a 0.85" GC9107-driven LCD with specifications:

• Resolution: 128×80 pixels
• Interface: SPI@20MHz
• Color Depth: 16-bit RGB (565 format)
• Power Consumption: 80mW typical

Connection Scheme:

LCD Pin	MCU Pin	Function
SCL	GPIO10	SPI CLK
SDA	GPIO11	SPI MOSI
DC	GPIO12	Data/Cmd
RST	GPIO13	Reset
CS	GPIO14	Chip Select

Driver Development

Created custom driver with these features:

• Double buffering implementation
• DMA-accelerated transfers
• LVGL integration for GUI development

Key driver functions:

#include "esp_timer.h"
#include "esp_err.h"
#include "esp_log.h"
#include "esp_check.h"

#include "openGlasses.h"

static const char *TAG = "openGlasses";

static lv_disp_t *lvgl_disp = NULL;
static esp_lcd_panel_io_handle_t panel_io_handle = NULL;
static esp_lcd_panel_handle_t panel_handle = NULL;

void bsp_lvgl_rounder_cb(struct _lv_disp_drv_t *disp_drv, lv_area_t *area)
{
    uint16_t x1 = area->x1;
    uint16_t x2 = area->x2;

    // round the start of coordinate down to the nearest 4M number
    area->x1 = (x1 >> 2) << 2;
    // round the end of coordinate up to the nearest 4N+3 number
    area->x2 = ((x2 >> 2) << 2) + 3;
}

esp_err_t bsp_spi_bus_init(void)
{
    static bool initialized = false;
    if (initialized)
    {
        return ESP_OK;
    }

    const spi_bus_config_t spi_cfg = {
        .mosi_io_num = BSP_SPI2_MOSI,
        .miso_io_num = BSP_SPI2_MISO,
        .sclk_io_num = BSP_SPI2_SCLK,
        .quadwp_io_num = -1,
        .quadhd_io_num = -1,
        .isr_cpu_id = 0,
        .max_transfer_sz = 4095,
    };
    BSP_ERROR_CHECK_RETURN_ERR(spi_bus_initialize(SPI2_HOST, &spi_cfg, SPI_DMA_CH_AUTO));

    initialized = true;
    return ESP_OK;
}

esp_err_t bsp_lcd_brightness_set(int brightness_percent)
{
    if (brightness_percent > 100)
    {
        brightness_percent = 100;
    }
    if (brightness_percent < 0)
    {
        brightness_percent = 0;
    }

    ESP_LOGD(TAG, "Setting LCD backlight: %d%%", brightness_percent);
    uint32_t duty_cycle = (BIT(BSP_LCD_LEDC_DUTY_RES) * (brightness_percent)) / 100;
    BSP_ERROR_CHECK_RETURN_ERR(ledc_set_duty(LEDC_LOW_SPEED_MODE, BSP_LCD_LEDC_CH, duty_cycle));
    BSP_ERROR_CHECK_RETURN_ERR(ledc_update_duty(LEDC_LOW_SPEED_MODE, BSP_LCD_LEDC_CH));

    return ESP_OK;
}

static esp_err_t bsp_lcd_backlight_init()
{
    const ledc_channel_config_t backlight_channel = { .gpio_num = BSP_LCD_BL,
        .speed_mode = LEDC_LOW_SPEED_MODE,
        .channel = BSP_LCD_LEDC_CH,
        .intr_type = LEDC_INTR_DISABLE,
        .timer_sel = LEDC_TIMER_1,
        .duty = BIT(BSP_LCD_LEDC_DUTY_RES),
        .hpoint = 0 };
    const ledc_timer_config_t backlight_timer = { .speed_mode = LEDC_LOW_SPEED_MODE, .duty_resolution = BSP_LCD_LEDC_DUTY_RES, .timer_num = LEDC_TIMER_1, .freq_hz = 5000, .clk_cfg = LEDC_AUTO_CLK };
    BSP_ERROR_CHECK_RETURN_ERR(ledc_timer_config(&backlight_timer));
    BSP_ERROR_CHECK_RETURN_ERR(ledc_channel_config(&backlight_channel));

    BSP_ERROR_CHECK_RETURN_ERR(bsp_lcd_brightness_set(100));

    return ESP_OK;
}

static esp_err_t bsp_lcd_pannel_init(esp_lcd_panel_handle_t *ret_panel, esp_lcd_panel_io_handle_t *ret_io)
{
    esp_err_t ret = ESP_OK;

    ESP_LOGD(TAG, "Install panel IO");
    const esp_lcd_panel_io_spi_config_t io_config = {
        .dc_gpio_num = BSP_LCD_DC,
        .cs_gpio_num = BSP_LCD_CS,
        .pclk_hz = BSP_LCD_PIXEL_CLK_HZ,
        .lcd_cmd_bits = BSP_LCD_CMD_BITS,
        .lcd_param_bits = BSP_LCD_PARAM_BITS,
        .spi_mode = 0,
        .trans_queue_depth = 10,
    };
    ESP_GOTO_ON_ERROR(esp_lcd_new_panel_io_spi((esp_lcd_spi_bus_handle_t)BSP_LCD_SPI_NUM, &io_config, ret_io), err, TAG, "New panel IO failed");

    ESP_LOGD(TAG, "Install LCD driver");

    const esp_lcd_panel_dev_config_t panel_config = {
        .reset_gpio_num = BSP_LCD_RST, // Shared with Touch reset
        .rgb_ele_order = BSP_LCD_RGB_ELEMENT_ORDER,
        .bits_per_pixel = BSP_LCD_BITS_PER_PIXEL,
    };

    ESP_GOTO_ON_ERROR(esp_lcd_new_panel_gc9107(*ret_io, (const esp_lcd_panel_dev_config_t *)&panel_config, ret_panel), err, TAG, "New panel failed");

    esp_lcd_panel_reset(*ret_panel);
    esp_lcd_panel_init(*ret_panel);
    esp_lcd_panel_invert_color(*ret_panel, true);
    esp_lcd_panel_set_gap(*ret_panel, 2, 1);

    return ESP_OK;

err:
    if (*ret_panel)
    {
        esp_lcd_panel_del(*ret_panel);
    }
    if (*ret_io)
    {
        esp_lcd_panel_io_del(*ret_io);
    }
    spi_bus_free(BSP_LCD_SPI_NUM);

    return ret;
}

static lv_disp_t *bsp_display_lcd_init(const bsp_display_cfg_t *cfg)
{
    assert(cfg != NULL);

    ESP_LOGD(TAG, "Initialize SPI bus");
    if (bsp_spi_bus_init() != ESP_OK)
        return NULL;

    ESP_LOGD(TAG, "Initialize LCD panel");

    if (bsp_lcd_pannel_init(&panel_handle, &panel_io_handle) != ESP_OK)
        return NULL;

    /* Add LCD screen */
    ESP_LOGD(TAG, "Add LCD screen");
    const lvgl_port_display_cfg_t disp_cfg = {
        .io_handle = panel_io_handle,
        .panel_handle = panel_handle,
        .buffer_size = cfg->buffer_size,
        .double_buffer = cfg->double_buffer,
        .hres = BSP_LCD_H_RES,
        .vres = BSP_LCD_V_RES,
        .monochrome = false,
        .rotation = {
            .swap_xy = BSP_LCD_SWAP_XY,
            .mirror_x = BSP_LCD_MIRROR_X,
            .mirror_y = BSP_LCD_MIRROR_Y,
        },
        .flags = {
            .buff_dma = cfg->flags.buff_dma,
            .buff_spiram = cfg->flags.buff_spiram,
#if LVGL_VERSION_MAJOR == 9 && defined(CONFIG_LV_COLOR_16_SWAP)
            .swap_bytes = true,
#endif
        }};

    return lvgl_port_add_disp(&disp_cfg);
}

lv_disp_t *bsp_lvgl_init(void)
{
#ifdef CONFIG_HEAP_ABORT_WHEN_ALLOCATION_FAILS
    BSP_ERROR_CHECK_RETURN_NULL(heap_caps_register_failed_alloc_callback(heap_caps_alloc_failed_hook));
#endif
    bsp_display_cfg_t cfg = { .lvgl_port_cfg = ESP_LVGL_PORT_INIT_CONFIG(),
        .buffer_size = BSP_LCD_H_RES * LVGL_DRAW_BUFF_HEIGHT,
        .double_buffer = LVGL_DRAW_BUFF_DOUBLE,
        .flags = {
            .buff_dma = false,
            .buff_spiram = true,
        } };
    cfg.lvgl_port_cfg.task_priority = CONFIG_LVGL_PORT_TASK_PRIORITY;
    cfg.lvgl_port_cfg.task_affinity = CONFIG_LVGL_PORT_TASK_AFFINITY;
    cfg.lvgl_port_cfg.task_stack = CONFIG_LVGL_PORT_TASK_STACK_SIZE;
    cfg.lvgl_port_cfg.task_max_sleep_ms = CONFIG_LVGL_PORT_TASK_MAX_SLEEP_MS;
    cfg.lvgl_port_cfg.timer_period_ms = CONFIG_LVGL_PORT_TIMER_PERIOD_MS;
    return bsp_lvgl_init_with_cfg(&cfg);
}

lv_disp_t *bsp_lvgl_init_with_cfg(const bsp_display_cfg_t *cfg)
{
    if (lvgl_port_init(&cfg->lvgl_port_cfg) != ESP_OK)
        return NULL;
    if (bsp_lcd_backlight_init() != ESP_OK)
        return NULL;
    lvgl_disp = bsp_display_lcd_init(cfg);
    if (lvgl_disp != NULL)
    {
        lvgl_disp->driver->rounder_cb = bsp_lvgl_rounder_cb;
    }
    return lvgl_disp;
}

lv_disp_t *bsp_lvgl_get_disp(void)
{
    return lvgl_disp;
}

esp_lcd_panel_handle_t bsp_lcd_get_panel_handle(void)
{
    return panel_handle;
}

#include "esp_err.h"
#include "esp_log.h"
#include "esp_check.h"

#include "openGlasses.h"

#include "lv_demos.h"

static const char *TAG = "app_main";

static lv_disp_t *lvgl_disp = NULL;

void app_main(void)
{
    lvgl_disp = bsp_lvgl_init();
    assert(lvgl_disp != NULL);

    // Lock the mutex due to the LVGL APIs are not thread-safe
    if (lvgl_port_lock(0))
    {
        lv_demo_benchmark();    /* A demo to measure the performance of LVGL or to compare different settings. */
        lvgl_port_unlock();
    }

    while (1)
    {
        printf("free_heap_size = %ld\n", esp_get_free_heap_size());
        vTaskDelay(1000 / portTICK_PERIOD_MS);
    }
}

tip

Driver source code: GC9107 Driver Implementation

Demonstration

Here's the consolidated challenges section with unified formatting:

---

1.3. Challenges & Solutions

1.3.1 Audio Module

1. Clock Jitter Issues

• Symptom: Intermittent audio distortion
• Fix:
  • Implemented software clock recalibration routine

2. Network Streaming Stability

• Symptom: Frequent buffer underruns
• Solution:
  • Dual-buffer design (5s pre-cache + active buffer)

1.3.2 Display Module

1. SPI Signal Integrity

• Issue: Screen tearing at 40MHz
• Solution:
  • Reduced SPI clock frequency to 20MHz

2. Power Optimization

• Problem: 120mA backlight current
• Improvements:
  • Ambient light sensor integration
  • Dynamic refresh rate (1-60Hz)

1.4. Resources

Code Repositories

• Main Project Repository

Technical References

1. MAX98357A Datasheet
2. GC9107 Programming Guide
3. PCB